1. Field of the Invention
This invention relates to the field of information storage utilizing rigid disks, and more particularly to apparatus for dynamically loading and unloading read/write magnetic recording elements for flight above the surface of moving magnetic media.
2. Description of the Prior Art
In certain types of disk files which include rigid magnetic media it is desirable to load and unload a magnetic recording reproducing element into flight above the surface of the moving media as opposed to utilizing take off from and landing on the magnetic media where the magnetic recording element comes to rest on the disk after rotation has ceased and takes off from the disk after the disk is once again spun up. U.S. Pat. No. 4,535,374 to Anderson et al., issued Aug. 13, 1985, is exemplary of a rigid disk drive of the linear actuator type which provides for dynamic loading of magnetic read/write heads above the surface of a disk. In Anderson et al. a stationary cam follower is provided on and supported from the housing, and the load arm, which includes a magnetic recording head at its free end, is provided with a cam surface intermediate the free end and the end supported by the actuator. The cam surface cooperates with a stationary cam to lift the head above the surface of the disk when the head arm is retracted.
Another linear actuator rigid disk drive utilizing a cam arrangement to achieve dynamic loading of the magnetic recording head above the disk is illustrated in U.S. Pat. No. 4,663,682 to McNeil, issued May 5, 1987. In McNeil, a pair of cam surfaces are supported by the disk drive housing and a wing, having a pair of free ends, is attached to the load beam intermediate the actuator driving mechanism and the free end of the load beam which supports the head slider. The free ends of the wing cooperate with the cam surfaces to lift the magnetic recording head slider above the surface of the disk when the head arm is retracted. In McNeil, the direction of movement of the magnetic media beneath the magnetic recording head is such that the media is moving in a direction which is parallel to the longitudinal axis of the slider on which the magnetic recording element is supported and perpendicular to the longitudinal axis of load beam. The cam surfaces in McNeil are offset and provide pitch to the slider during the loading process when the slider is approaching the surface of the rotating media.
U.S. Pat. No. 4,933,785 to Morehouse et al., issued Jun. 12, 1990, and assigned to Prairietek Corporation, discloses a magnetic disk drive utilizing a rotary actuator. The load beams (which support the read/write elements) each include a lift button which is supported on the load beam, and positioned on the longitudinal axis of the load beam. The lift buttons cooperate with a spreader, which includes cam surfaces, to provide dynamic loading and unloading of the slider which is supported on the end of the load beam opposite of the pivot point of the load beam. The buttons and the cooperating spreader with cam surfaces are located intermediate the pivot point of the rotary actuator and the magnetic head. The button and cam surface on the spreader provide a symmetrical lift to the load beam and correspondingly symmetrical loading of the magnet head above the media, which in this configuration is rotating in the direction beneath the head which is substantially parallel to the longitudinal axis of the load beam which is supporting the slider.
A later introduced rigid disk drive from Prairietek Corporation, utilized a dynamic loading structure having a cam surface supported on the housing which contacted directly the load beam of the rotary arm having the magnetic slider on its free end. In this Prairietek hard disk drive, denominated the model 120, the cam is supported on the housing and is positioned intermediate the head slider and the pivot point of the rotary actuator. The principle distinction between the dynamic loading structure in the model 120 over the structure illustrated in the '785 patent is the elimination of the button which was included on the load beam and provided a center line lift on the load beam. In the model 120 disk drive a heavy roll torque is applied to the load beam and there is no ability to change the amount of torque and correspondingly the roll applied to load beam.
U.S. Pat. No. 3,984,873, issued Oct. 5, 1976 to Pejcha illustrates a structure for dynamically loading heads, which in one embodiment utilizes a movable channel member which is supported above the surface of the rotating rigid disk. The loading of a head above the surface of the disk is achieved by providing flat spring extensions which extend symmetrically from the free end of the load beam and are captured in the channel which is positioned in a plane above the surface of the disk such that the opening is generally parallel to the plane of the disk. With the spring extensions captured in the channel, the heads are prevented from being loaded on the disk. To load the heads the channel member is moved out of contact with the flat spring extensions and the heads move toward the surface of the associated disk. In another embodiment, the flat spring extensions on the ends of the load beam are crisscrossed and a pivoted member is moved into contact with the crisscrossed free ends to unload the heads from the disk. In a third embodiment, a cam surface is provided adjacent to the edge of the rotating disk and the magnetic head is supported on a spring member which is affixed by bolts to a rotating arm. An extension of the spring member on the end adjacent to the magnetic head is positioned at right angles with respect to the center line of the rotary arm on which the head and spring is mounted, with the spring extension having a longitudinal axis which is parallel to the longitudinal axis of the cam surface.
U.S. Pat. No. 5,027,241, issued Jun. 25, 1991 to Hatch et al. illustrates a rotary actuator using a dynamic loading tab which extends from the end of the load beam. In Hatch et al., the load tab (which cooperates with a cam for loading and unloading the slider from the surface of the disk) extends outwardly from the end of the load beam and is symmetrically aligned with the centerline of the load beam. Although this provides geometric symmetry, it does not provide zero torque on the load beam as it is lifted from the disk. In contrast, in accordance with one embodiment of the present invention an asymmetrically positioned lift tab is used whereby the amount of roll provided to the slider as it is lifted from the surface of the disk can be fine tuned to an optimum level. In a second embodiment of the present invention a lift tab structure which provides a zero torque force on the load beam is provided. This is achieved by utilizing an offset load tab.
A number of the prior disk drives employing dynamic head loading utilized a cam arrangement in which a portion of the cam extended over the surface of the magnetic recording disk. With the continuing desire to produce disk drives which are more compact, the requirement of having a portion of the cam surface extend above the surface of the disk made it more difficult to reduce the disk-to-disk spacing, and accordingly more difficult to reduce the height of the disk drive. Additionally, this requirement made it more difficult to design an effective cam in view of constraints, such as, the type of material from which the cam could be constructed. This is particularly troublesome in drives using a plurality of disks where all of the disk surfaces are used for storing information. Additionally, in disk drives in which a portion of the cam surface extended above the magnetic disk, assembly of the drive was made somewhat more difficult since if the cam assembly were installed prior to installation of the magnetic disks in the housing, it was necessary to either pivot the cam assembly out of the way of the disks during installation or to install the cam assembly after the disks had been installed. In accordance with one embodiment of the present invention, a cam assembly is provided which is constructed such that no portion of the cam assembly extends over a surface of any of the recording disks, thus eliminating the necessity to take special precautions when installing the magnetic disks, and secondly eliminating the necessity of providing space for portions of the cam surfaces between adjacent disks.